Erica had 30 dollars to spend on 3 gifts. She spent 10 7 10 dollars on gift A and 6 2 5 dollars on gift B. How much money did she have left for gift C? PLZ HELP

I'm stuck on this :

Plz answer asap! i will reward brainliest and 12 points for these three questions!take notice: these three questions are completely different! 1) what is the percentage of sugar in the syrup made of 10 kg of water and 4 kg of suugar? 2) what was the original price if after 10% discount it became $450? 3) at first a price was decreased by 12%, then it was disounted again by an additional 5%. what is the percent of the total discount? , and remeber i will award brainliest and 12 points!